The present invention relates to lighters disposed in motor vehicles and, more particularly, to overheating safety devices for such lighters.
Automotive vehicles more recently have plastic instrumentation boards in which the cigarette lighters are installed. In the event that the lighter has some electrical breakdown and excessive heat is generated by the lighter, it is desired to have overheating safety devices so that the plastic instrumentation board is not damaged.
One prior art approach for protecting the vehicle lighter is known in U.S. Pat. No. 3,662,153. There, it is disclosed that the current-carrying bimetal springs arranged in the socket of the lighter and in the housing of the grounded socket, can create a short circuit upon overheating of the lighter, after insertion of the lighter element. The bimetal springs, therefore, serve on the one hand to heat the glow element arranged on the plug of the lighter, and on the other hand, to create the short circuit on overheating. In the latter instance, an electrical fuse is affected which cuts off the supply of electrical current to the lighter. This known overheating safety device is still effective, however, if one of the two bimetal springs arranged in the socket fails. The other bimetal spring is still effective to provide a complete circuit with the electrical fuse. If both bimetal springs fail, however, the protection fails also. Furthermore, since the bimetal springs have two contact positions (it is necessary to switch from the glow element to the housing in the case of overheating) an exact and time-consuming adjustment of the bimetal springs is necessary. This is quite costly in mass production.